"Soon" we will get 2 new demons; what will be the role for each of them ? What position will the felguard/wrathguard will be, being them aviable to all spec? Actually we are fine, i may agree, but i do think this may be the right time to think better than reintroducing 2 vanilla pets without a clear balance in powers and roles; and, to be honest, reaching lvl 100, i'd prefere some different demon than the old ones.
This is not a community issue that i want to solve mechanical, or so i think.

I do remember the good old days when I could just sacrifice those bastards for extra power in BC and I welcomed the change here as well.
I for one belong to the camp of those who don't like pets that much anymore. It was fun at the beginning but they are more pain in the as than they are worth. I still remember the nightmarish usage of Succubus in early Cata when it was top dps for a short while and at the same time it provided the worst possible demon soul effect ever in existence ( +10% SB damage???? REALLY????).
That being said the pets bugging out on various fights ( Elegon/Sha/Durumu) didn't help either, so I am really happy we have a choice for a Sac talent. Now I only use them for soloing LK HC, Yogg Alone and such shenanigans, otherwise nom nom, give me your power. While they granted great utility first in PvP they made the warlocks a bit vulnerable, of course losing your pet was not the end of the world, but regaining it was a waste of resources. That being said this is a personal point of view.

Quick thing though; You'll never get a Nathrezim as a pet, a Pit Lord maybe, but a Nathrezim nope. If anything; *you'll* be a Nathrezim pet.

i agree you'll never be aloud to control a Nathrezim they are the Dread Lords and are powerful demons in Warcraft lore they would end up controling you or killing you, and like that gnome warlock in Totc that summons the Eredar.. those types of demons are just to powerful, although an Annihilan Pit Lord is more plausible but they're powerful to and only two Pit Lords in the game are able to be controlled with Enslave Demon that I know of, one on mount Hyjal and the other is in the Kanrethad fight.. it would be cool to see a limited time Pit Lord summon with a CD and the Doomguard/Terrorguard and the Infernal/Abyssal become normal summons, there is also the Void Terror's if you remember Immol'thar from Diremaul and Occu'thar from Baradin Hold, i see no reason not being able to summon those demons and it would be interesting, maybe they could shoot eye lasers..

I think pets now have very nicely ditributed roles. The only thing I would like to change is to have Grimoire of Service let you summon 2 of old minions permanently (at 60% dps per pet) rather than a cooldown. Currently GoServ serve as a way for Demo locks to get extra energy on pull and more aoe damage (since it's only minion with damaging cd move), and even then, for fights w/o aoe every 2 min, GoSup is just as good. Every guide recommend Sup or Sac. Does high end pvp'ers actually use Serv for extra disarm/silence/dispell? Seems like intended role of it, but I can't imagine macro that will allow you to access every of those skill quickly and precisly.

Having perma 2 minion GoServ giving same dps (+slightly lower cd on specials?) as single superior minion GoSup would be imo more interesting choice than it is current.

I do think the 2 new talented demons are going to impact roles and balance, they have to "weight" a lvl 100.

I cannot understand why ppl keep talking about Nathrezim are too powerful as pets...Annihilan are generals, doomguards too (Kazzak) while in Well of Eternity you can find entire pull of "Dreadlords", even wondering in low lvl zones, and in Outland; for sure, lore account them as one of the races responsible for Sargeras corruption, but since then they have always served as lackeys to a more powerful entity (KJ and Archimonde) and the strongest of theyr kind have been killed by Illidan just after the consumption of the skull of Guldan, they are far from being "too powerfull", and I think they should be a perfect choice for the role of Control/utility/affliction friendly Demon as an upgrade to the existing ones.

On the other hand, i cannot understand wich role will a Doomguard and an Infernal will take aside from "more DPS/ more AoE DPS".